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[libvirt] [PATCH] lxc: Add virCgroupSetOwner()



From: Richard Weinberger <richard nod at>

Add a new helper function to change the permissions of a control
group. This function is needed for user namespaces, we need to
chmod() the cgroup to the initial uid/gid such that systemd is
allowed to use the cgroup.

Only the systemd controller is made accessible to the container.
Others must remain read-only since it is generally not safe
to delegate resource controller write access to unprivileged
processes.

Signed-off-by: Richard Weinberger <richard nod at>
---
 src/libvirt_private.syms |  1 +
 src/lxc/lxc_cgroup.c     |  9 ++++++++
 src/util/vircgroup.c     | 54 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/util/vircgroup.h     |  5 +++++
 4 files changed, 69 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 0b28bac..cfa9f75 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1056,6 +1056,7 @@ virCgroupSetMemory;
 virCgroupSetMemoryHardLimit;
 virCgroupSetMemorySoftLimit;
 virCgroupSetMemSwapHardLimit;
+virCgroupSetOwner;
 virCgroupSupportsCpuBW;
 
 
diff --git a/src/lxc/lxc_cgroup.c b/src/lxc/lxc_cgroup.c
index cc0d5e8..0d0d9c0 100644
--- a/src/lxc/lxc_cgroup.c
+++ b/src/lxc/lxc_cgroup.c
@@ -484,6 +484,15 @@ virCgroupPtr virLXCCgroupCreate(virDomainDefPtr def)
                             &cgroup) < 0)
         goto cleanup;
 
+    /* setup control group permissions for user namespace */
+    if (def->idmap.uidmap) {
+        if (virCgroupSetOwner(cgroup,
+                              def->idmap.uidmap[0].target,
+                              def->idmap.gidmap[0].target,
+                              (1 << VIR_CGROUP_CONTROLLER_SYSTEMD)))
+            goto cleanup;
+    }
+
 cleanup:
     return cgroup;
 }
diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
index a6d60c5..2dc6986 100644
--- a/src/util/vircgroup.c
+++ b/src/util/vircgroup.c
@@ -3253,6 +3253,60 @@ cleanup:
 }
 
 
+int virCgroupSetOwner(virCgroupPtr cgroup,
+                      uid_t uid,
+                      gid_t gid,
+                      int controllers)
+{
+    size_t i;
+
+    for (i = 0; i < VIR_CGROUP_CONTROLLER_LAST; i++) {
+        char *base, *entry;
+        DIR *dh;
+        struct dirent *de;
+
+        if (!((1 << i) & controllers))
+            continue;
+
+        if (!cgroup->controllers[i].mountPoint)
+            continue;
+
+        if (virAsprintf(&base, "%s%s", cgroup->controllers[i].mountPoint,
+            cgroup->controllers[i].placement) < 0) {
+                virReportOOMError();
+                return -1;
+        }
+
+        dh = opendir(base);
+        while ((de = readdir(dh)) != NULL) {
+            if (STREQ(de->d_name, ".") ||
+                STREQ(de->d_name, ".."))
+                continue;
+
+            if (virAsprintf(&entry, "%s/%s", base, de->d_name) < 0) {
+                VIR_FREE(base);
+                virReportOOMError();
+            }
+
+            if (chown(entry, uid, gid) < 0)
+                virReportSystemError(errno, _("cannot chown '%s' to (%u, %u)"),
+                    entry, uid, gid);
+
+            VIR_FREE(entry);
+        }
+        closedir(dh);
+
+        if (chown(base, uid, gid) < 0)
+            virReportSystemError(errno, _("cannot chown '%s' to (%u, %u)"),
+                base, uid, gid);
+
+        VIR_FREE(base);
+    }
+
+    return 0;
+}
+
+
 /**
  * virCgroupSupportsCpuBW():
  * Check whether the host supports CFS bandwidth.
diff --git a/src/util/vircgroup.h b/src/util/vircgroup.h
index a70eb18..38d94f3 100644
--- a/src/util/vircgroup.h
+++ b/src/util/vircgroup.h
@@ -225,4 +225,9 @@ int virCgroupIsolateMount(virCgroupPtr group,
 
 bool virCgroupSupportsCpuBW(virCgroupPtr cgroup);
 
+int virCgroupSetOwner(virCgroupPtr cgroup,
+                      uid_t uid,
+                      gid_t gid,
+                      int controllers);
+
 #endif /* __VIR_CGROUP_H__ */
-- 
1.8.5.3


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